Chlamydophila species

  • Diagnosis
  • Background
  • Lab Tests
  • References
  • Related Content

Indications for Testing

  • C. pneumoniae – atypical pneumonia presentation
  • C. psittaci – atypical pneumonia and history of bird exposure

Laboratory Testing

  • Chlamydophila pneumoniae infection (CDC, 2014)
  • Psittacosis (CDC, 2014)
  • Initial testing
    • CBC with differential
  • Serology
    • Atypical pneumonia presentation
      • Order C. pneumoniae, M. pneumoniae and Legionella pneumophila concurrently; routine diagnostic tests to identify etiologic agent of outpatient pneumonia in adults is optional (Infectious Disease Society of America/American Thoracic Society)
      • Confirmed by paired serology for C. pneumoniae (four-fold elevation)
      • PCR – much more sensitive than culture and serology
      • Culture – difficult to grow atypical agents; positive culture confirms diagnosis
    • Suspicion for C. psittaci
      • Order antibody panel if suspicious of C. psittaci
      • Performed using complement fixation, microimmunofluorescence, enzyme immunoassay

Imaging Studies

  • Chest x-ray – no distinctive chest x-ray pattern

Differential Diagnosis

Chlamydophila is a genus of bacteria in the Chlamydiaceae family that causes atypical pneumonias, which may become life threatening.


  • Incidence
  • Age
    • C. pneumoniae – peak incidence is late childhood to young adulthood
      • ~50% of young adults in the U.S. will have evidence of past infection by age 20
      • Reinfection throughout life is common
  • Transmission
    • C. pneumoniae – respiratory secretions
      • May produce epidemics in close-quarter settings such as military barracks, prisons
    • C. psittaci – respiratory inhalation of dried secretions during exposure to infected birds (zoonoses)
      • Does not require prolonged contact with infected bird
      • May be an occupation-related disease


  • C. psittaci and C. pneumoniae are obligate, intracellular, gram-negative bacteria

Clinical Presentation

  • C. pneumoniae
    • Incubation – 7-10 days
    • Constitutional – leukocytosis and fever are often lacking; may resemble Mycoplasma pneumoniae infections
    • Pulmonary – cough, bronchitis, pneumonia, exacerbations of chronic bronchitis and asthma
    • Upper respiratory tract – laryngitis, otitis media, sinusitis, pharyngitis
    • Dermatologic – erythema nodosum
    • Neurologic – meningitis (uncommon)
    • Cardiac – endocarditis, myocarditis (uncommon)
  • C. psittaci
    • Incubation – 5-19 days
    • Constitutional – fever, chills, headache, myalgias
    • Pulmonary – dry cough, pleural rub, rales, dyspnea, pneumonia
    • Gastrointestinal – diarrhea, nausea, anorexia, abdominal pain
    • Hepatitic – hepatitis
    • Dermatologic – faint macular rash may occur (Horder spots), erythema multiforme, erythema nodosum
    • Neurologic – cranial nerve palsies, cerebellar involvement, transverse myelitis, meningitis
    • Cardiac – endocarditis, myocarditis, pericarditis

Indications for Laboratory Testing

Tests generally appear in the order most useful for common clinical situations.
Click on number for test-specific information in the ARUP Laboratory Test Directory

Chlamydia pneumoniae by PCR 0060715
Method: Qualitative Polymerase Chain Reaction

Chlamydia Antibody Panel, IgG & IgM by IFA 0065100
Method: Semi-Quantitative Indirect Fluorescent Antibody


Anti-chlamydial IgM antibody is very cross-reactive and will often represent titers to multiple, non-infecting chlamydial species

Follow Up

If results are equivocal, retest sera 2-3 weeks after first test

Mycoplasma pneumoniae Antibodies, IgG & IgM 0050399
Method: Semi-Quantitative Enzyme-Linked Immunosorbent Assay

Legionella pneumophila Antigen, Urine 0070322
Method: Qualitative Enzyme-Linked Immunosorbent Assay

Additional Tests Available

CBC with Platelet Count and Automated Differential 0040003
Method: Automated Cell Count/Differential


May help differentiate between bacterial and viral pneumonias

Chlamydia Antibody Panel, IgG by IFA 0065139
Method: Semi-Quantitative Indirect Fluorescent Antibody

Chlamydia Antibody Panel, IgM by IFA 0065105
Method: Semi-Quantitative Indirect Fluorescent Antibody

Mycoplasma pneumoniae by PCR 0060256
Method: Qualitative Polymerase Chain Reaction


Evaluate for Chlamydia infection

Legionella Species by Qualitative PCR 2010125
Method: Qualitative Polymerase Chain Reaction


Rapid diagnostic test for Legionella, particularly in patient partially treated with empirical antibiotics

General References

Blasi F, Tarsia P, Aliberti S. Chlamydophila pneumoniae. Clin Microbiol Infect. 2009; 15(1): 29-35. PubMed

Burillo A, Bouza E. Chlamydophila pneumoniae. Infect Dis Clin North Am. 2010; 24(1): 61-71. PubMed

Cunha B. The atypical pneumonias: clinical diagnosis and importance. Clin Microbiol Infect. 2006; 12 Suppl 3: 12-24. PubMed

Forgie S, Marrie T. Healthcare-associated atypical pneumonia. Semin Respir Crit Care Med. 2009; 30(1): 67-85. PubMed

Johansson N, Kalin M, Tiveljung-Lindell A, Giske C, Hedlund J. Etiology of community-acquired pneumonia: increased microbiological yield with new diagnostic methods. Clin Infect Dis. 2010; 50(2): 202-9. PubMed

Kumar S, Hammerschlag M. Acute respiratory infection due to Chlamydia pneumoniae: current status of diagnostic methods. Clin Infect Dis. 2007; 44(4): 568-76. PubMed

Villegas E, Sorlózano A, Gutiérrez J. Serological diagnosis of Chlamydia pneumoniae infection: limitations and perspectives. J Med Microbiol. 2010; 59(Pt 11): 1267-74. PubMed

Wolf J, Daley A. Microbiological aspects of bacterial lower respiratory tract illness in children: atypical pathogens. Paediatr Respir Rev. 2007; 8(3): 212-9, quiz 219-20. PubMed

References from the ARUP Institute for Clinical and Experimental Pathology®

Kendall B, Tardif K, Schlaberg R. Chlamydia trachomatis L serovars and dominance of novel L2b ompA variants, U.S.A. Sex Transm Infect. 2014; 90(4): 336. PubMed

Medical Reviewers

Last Update: February 2016